A communication link (e.g. between node A and node B) with the capability to support the connection in both directions at the same time is called full-duplex, or two-way. In contrast, a link that can support the connection in only one direction at a time is called one-way or half-duplex.
Current wireless systems are one-way and rely on either separate time slots (Time Division Duplex, TDD) or separate frequency bands (Frequency Division Duplex, FDD) to transmit and to receive. These alternatives have their relative pros and cons, but both suffer from lack of ability to transmit and to receive simultaneously and over the entire frequency band. Full-duplex capability is particularly useful when several wireless nodes share a frequency band, as it helps in managing the impact of multi-user interference, maximizing spectral efficiency, and improving network quality of service.
Point-to-point communications primarily concerns transmission between a single transmitter and a single receiver, while networking concerns scenarios where more than two users share the channel. The impact of full-duplex links in point-to-point communications is limited to doubling the rate by providing two symmetrical pipes of data flowing in opposite directions. This affects the point-to-point throughput with no direct impact on networking. In contrast, in multi-user wireless systems, due to the nature of transmission that everyone hears everyone else, full-duplex capability provides new ways to facilitate sharing of a common spectrum.
A basic feature of wireless transmission is that the transmission media is shared among all users and everyone hears everyone else. This feature can cause harmful effects in terms of multi-user interference and normally necessitates sophisticated network management. Full-duplex capability with support for asynchronous clients provides the means to benefit from the same basic feature of wireless transmission and facilitate network management.
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